Low dropout (LDO) regulators are DC linear voltage regulators that are commonly used to supply voltages to various components in electronic devices. LDO regulators are characterized by a small input to output differential (“dropout”) voltage, high efficiency and low heat dissipation.
Referring to FIG. 1, depicted is a schematic diagram of a conventional low dropout (LDO) voltage regulator 100. The LDO voltage regulator 100 includes a feedback circuit 102 including an error amplifier 110, feedback network 114, a stable voltage reference 108, and pass element 112. The pass element 112 may comprise a FET or BJT transistor.
The purpose of the LDO voltage regulator is to maintain a desired voltage at node VOUT when in a regulation mode of operation. The error amplifier 110 compares a sample of the VOUT voltage, fed via feedback network 114 (i.e., voltage divider comprising resistors 120, 122) into the positive input of the error amplifier 110, with a reference voltage from 108 fed into the negative input of the error amplifier 110.
If the voltage that is fed back is lower than the reference voltage, the pass element 112 increases the output voltage. If the feedback voltage is higher than the reference voltage, the pass element decreases the output voltage.
The input and output capacitors 115, 116 reduce the circuit's sensitivity to noise as well as, in the case of the output capacitor 116, affecting the stability of the control loop and the circuit's response to changes in load current.
Typically, the feedback circuit 102 comprises an integrated circuit, while the input and output capacitors 115, 116 are external to the integrated circuit. The output capacitor 116 may have a value in the microfarad range and thus is relatively large. This can occupy a significant amount of “board space” and may require an output pin from the integrated circuit. Also, a capacitor may be relatively expensive, particularly where a capacitor with a low ESR (equivalent series resistance) is required.